Patent application title: METHOD FOR IMPROVING HYDROCARBON-WATER COMPATIBILITY IN A SUBSURFACE HYDROCARBON-CONTAMINATED SITE

Abstract:

The present invention relates to methods for improving hydrocarbon-water
compatibility. More specifically, the invention relates to methods for
enhancing the production of surface-active agents in hydrocarbon-exposed
surface waters in order to improve hydrocarbon-water compatibility.
Hydrocarbon-exposed surface waters having enhanced levels of
surface-active agents can be used to improve remediation of subsurface
hydrocarbon-contaminated sites.

Claims:

1. A method for improving hydrocarbon-water compatibility in a subsurface
hydrocarbon-contaminated site:(a) obtaining a sample of
hydrocarbon-exposed surface water;(b) optionally supplementing the
surface water of (a) with at least one member selected from the group
consisting of (1) at least one carbon/energy source, (2) at least one
nitrogen source, and (3) a combination of (1) and (2), such that the
final molar ratio of carbon to nitrogen in the surface water of (a) is at
least about 6 to 1, thereby producing a supplemented surface water;(c)
incubating the hydrocarbon-exposed surface water of (a) or the
supplemented surface water of (b) under aerobic or anoxic conditions to
produce conditioned water having a desired level of surface-active
agents; and(d) injecting the conditioned water of (c) into said
subsurface hydrocarbon-contaminated site such that the conditioned water
comes in contact with hydrocarbons present at the site, thereby improving
said hydrocarbon-water compatibility.

2. The method of claim 1, wherein the final carbon to nitrogen ratio is at
least about 12 to 1.

3. The method of claim 2, wherein the final carbon to nitrogen ratio is at
least about 25 to 1.

4. The method of claim 1, wherein said incubating is carried out under
anoxic conditions.

8. The method of claim 1 or claim 4, wherein the nitrogen source is (1) at
least one soluble nitrate salt, (2) at least one soluble nitrite salt or
(3) a combination of at least one soluble nitrate salt and at least one
soluble nitrite salt.

9. The method of claim 8, wherein said soluble nitrate or nitrite salt is
a sodium, potassium, calcium or magnesium salt.

10. The method of claim 8, wherein the nitrogen source is nitrate.

11. The method of claim 1, wherein the desired level of surface-active
agents is determined using a determination of emulsion stability time.

12. The method of claim 1, wherein the desired level of surface-active
agents is determined by measuring surface tension.

13. The method of claim 1, wherein the desired level of surface-active
agents is the maximal level produced.

14. The method of claim 1, wherein the hydrocarbon-containing site
comprises oil.

15. The method of claim 1, wherein the hydrocarbon-containing site
comprises gasoline.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to methods for improving
hydrocarbon-water compatibility. More specifically, the invention relates
to methods for enhancing microbial growth and emulsifying activity in
order to improve hydrocarbon-water compatibility in a subsurface
hydrocarbon-contaminated site.

BACKGROUND OF THE INVENTION

[0002]Water and hydrocarbons such as oil and gasoline are incompatible
phases, thus a number of techniques, such as the use of surface-active
agents, have been studied in an effort to decrease the repellency between
water and said hydrocarbons. Surface-active agents are expected to be
useful for the remediation of shallow, subsurface sites that have been
contaminated with hydrocarbons. The introduction of surface-active agents
can be used to solubilize or mobilize hydrocarbons adsorbed to soil
particles or present as a separate hydrocarbon phase (see, for example,
West, C C and Harwell, J H, "Surfactants and Subsurface Remediation"
Environ. Sci. Techncl., 1992, 26(12):2324).

[0003]Some microbial products can decrease oil-water repellency because
they are surface active. Only certain groups of microorganisms are able
to produce these surface-active compounds (Neu, T. R (Microbiological
Reviews, 1996, 60:151-166). Such biologically produced surface-active
compounds have also been suggested for use in remediation of
hydrocarbon-contaminated sites. Many biologically produced surface-active
compounds are based on production by pure cultures of aerobic
microorganisms (for example, U.S. Pat. No. 4,522,261).

[0004]There exists a need for an inexpensive and effective method for
producing surface-active agents that can be used for improving
hydrocarbon-water compatibility, and thus for improving remediation of
hydrocarbon-contaminated subsurface sites.

SUMMARY OF THE INVENTION

[0005]The present invention provides a method for improving
hydrocarbon-water compatibility in a subsurface hydrocarbon-contaminated
site: [0006](a) obtaining a sample of hydrocarbon-exposed surface
water; [0007](b) optionally supplementing the surface water of (a) with
at least one member selected from the group consisting of (1) at least
one carbon/energy source, (2) at least one nitrogen source, and (3) a
combination of (1) and (2), such that the final molar ratio of carbon to
nitrogen in the surface water of (a) is at least about 6 to 1, thereby
producing a supplemented surface water; [0008](c) incubating the
hydrocarbon-exposed surface water of (a) or the supplemented surface
water of (b) under aerobic or anoxic conditions to produce conditioned
water having a desired level of surface-active agents; and [0009](d)
injecting the conditioned water of (c) into said subsurface
hydrocarbon-contaminated site such that the conditioned water comes in
contact with hydrocarbons present at the site, thereby improving said
hydrocarbon-water compatibility.

[0010]In additional embodiments, the carbon to nitrogen ratio is at least
about 12 to 1 and 25 to 1. Improved hydrocarbon-water compatibility is
useful for improving hydrocarbon-contaminant removal from subsurface
hydrocarbon-contaminated sites.

BRIEF DESCRIPTION OF THE FIGURES

[0011]FIG. 1 shows the treatment vials which were set up as described in
Example 1 and Table 3 after 8 days of growth.

[0012]FIG. 2 shows an example of stages in emulsion stability testing. A
control and a treatment vial are shown prior to, and subsequent to,
shaking.

DETAILED DESCRIPTION OF THE INVENTION

[0013]Waters exposed to hydrocarbons are common to oil reservoirs and
hydrocarbon-contaminated subsurface environments. Under appropriate
conditions, microorganisms in these waters are capable of producing
surface-active agents. The present invention utilizes exogenous, mixed
microbial populations present in surface waters that have been exposed to
hydrocarbons as a means of inexpensively generating surface-active agents
for improving hydrocarbon-water compatibility. According to embodiments
of the present invention, surface waters comprising said surface-active
agents can then be used to improve hydrocarbon contaminant removal from
hydrocarbon-contaminated subsurface sites.

[0014]The following definitional structure is provided for certain
terminology as employed in this specification:

[0015]"Remediation" is a process used to remove contaminants from a
contaminant-altered environment.

[0016]"Injection water" is water pumped down into a subsurface site for
pressure maintenance.

[0017]"Production water" is water associated with oil recovered from the
production well.

[0018]A "surface-active agent" is a material that can reduce the surface
tension of water in contact with a non-aqueous surface.

[0019]A "carbon/energy source" is an organic compound that provides both a
carbon source and an energy source for microbial cell growth.

[0020]An "injector well" is a well used in subsurface remediation to add
agents that will aid decontamination of groundwater and subsurface
formations.

[0021]An "interceptor well" is a well used to control local groundwater
flow gradients at remediation sites in order to minimize the movement of
contaminated material off site, usually by withdrawing liquid from the
subsurface formation.

[0022]"Conditioned water" is hydrocarbon-exposed water comprising a
desired level of surface-active agents.

[0023]"Emulsion stability time" is the time (in seconds, minutes, or
hours) that is required for oil-water emulsion droplets to completely
disappear to the unaided eye following a prescribed, vigorous shaking of
a two phase oil-water mixture.

[0024]"Hydrocarbon-water compatibility" refers to the degree to which the
surface tension of a hydrocarbon is reduced at the water-hydrocarbon
interface where lower surface tension equates with improved
hydrocarbon-water compatibility.

[0025]"Hydrocarbon-exposed surface water" refers to water at the land
surface that is in contact or has been in contact with a
hydrocarbon-containing site as defined herein.

[0026]"Hydrocarbon" refers to a molecule formed primarily by carbon and
hydrogen atoms. Examples include crude oil (crude petroleum) and
gasoline.

[0027]"Oil" refers to refined or crude petroleum.

[0028]In one embodiment, the present invention relates to a method for
improving hydrocarbon-water compatibility in a subsurface
hydrocarbon-contaminated site: [0029](a) obtaining a sample of
hydrocarbon-exposed surface water; [0030](b) optionally supplementing the
surface water of (a) with at least one member selected from the group
consisting of (1) at least one carbon/energy source, (2) at least one
nitrogen source, and (3) a combination of (1) and (2), such that the
final molar ratio of carbon to nitrogen in the surface water of (a) is at
least about 6 to 1, thereby producing a supplemented surface water;
[0031](c) incubating the hydrocarbon-exposed surface water of (a) or the
supplemented surface water of (b) under aerobic or anoxic conditions to
produce conditioned water having a desired level of surface-active
agents; and [0032](d) injecting the conditioned water of (c) into said
subsurface hydrocarbon-contaminated site such that the conditioned water
comes in contact with hydrocarbons present at the site, thereby improving
said hydrocarbon-water compatibility.

[0033]According to the present invention, a hydrocarbon-containing site is
a subsurface or subterranean site that harbors hydrocarbons. In one
embodiment, the hydrocarbon-containing site is a hydrocarbon-contaminated
site, where it is desired that remediation be used to remove the
hydrocarbon contaminants from said site. An example of a
hydrocarbon-contaminated site is the area surrounding a leaking
underground gasoline storage tank.

[0034]Hydrocarbon-exposed surface waters can in principle be any water
that has been exposed to hydrocarbons, preferably hydrocarbons having a
composition that approximates the composition of the
hydrocarbon-containing site. Examples of hydrocarbon-exposed surface
waters include oil-well associated surface waters, such as production
water or injection water. Examples also include groundwater
remediation-site injector well water, groundwater remediation site
interceptor well water, as well as wastewaters, surface waters from
hydrocarbon-contaminated sites, or run-off waters. The
hydrocarbon-exposed surface water need not be derived from the
hydrocarbon-containing site into which the conditioned water will be
injected, however economically this may be the preferred source.

[0035]In one embodiment, water from the hydrocarbon-containing site is
collected in a holding tank. The holding tank can be any suitable vessel
capable of holding the quantity of surface water to be conditioned under
the parameters required for conditioning, such as aeration. The water
should not have undergone any treatments that would kill or prevent the
growth of microbial populations, for example biocide treatment or heating
above 50° C.

[0036]According to the present invention, the growth and production of
surface-active agents by exogenous microorganisms can be stimulated in
hydrocarbon-exposed surface waters through the addition of appropriate
nutrients. Reports describing pure culture studies have shown that
biosurfactant production is dependent on the composition of the medium in
which the microorganism(s) grow (see, for example, Mercade, R. M. et al
1989. Biotechnology letters 11: 871 and Guera-Santos, L. H. et al,
Applied microbiology and biotechnology 24: 443). We have determined that
medium composition is similarly important for surface-active agent
production by mixed populations of exogenous microorganisms in waters
from hydrocarbon-exposed sites. Excess of carbon/energy source promotes
the production of surface-active agents.

[0037]In one embodiment, the at least one carbon/energy source that
results in production of surface-active agents by the microorganisms is
added to the water collected in the holding tank. The carbon/energy
supplement is added at greater than or equal to approximately 10 g per
liter. In one embodiment the carbon/energy supplement is added at
approximately 30 g to 60 g per liter. The appropriate at least one
carbon/energy source can be determined empirically by testing for
decreased surface tension following microbial growth as is known to those
skilled in the art, or can be determined by economic factors related to
cost and availability of carbon/energy sources. Examples of suitable
carbon/energy sources include soluble starch, potato starch, cornstarch
or other vegetable starches, propionate, acetate, vinegar, lactate, whey
solids, lactic acid, butyrate, butyric acid, glucose, high fructose corn
syrup, soybean oil, corn oil or olive oil. Propionate, acetate, lactate
and butyrate can be supplied as any suitable soluble salt, such as
sodium. Vinegar (acetic acid), lactic acid and butyric acid can be
neutralized to a pH suitable for microbial growth and/or production of
surface-active agents. In one embodiment, vinegar, lactic acid and
butyric acid are neutralized to a pH of about 4 to about 9; in another
embodiment, these acids are neutralized to a pH of about 6 to about 8.
These carbon/energy sources may be added to the holding tank individually
or in combination as long as the weight specification is met. The pH of
surface water is typically about 4 to about 9.

[0038]In one embodiment favoring anaerobic populations, a nitrate or
nitrite salt is added to the holding tank and the water is maintained
under anoxic conditions, wherein any headspace gas is a gas other than
air or oxygen. Sodium, potassium, calcium, magnesium, or other soluble
salts of nitrate or nitrite may be used individually or in combination.
Nitrate is added in an amount sufficient to induce surface-active agent
production. In one embodiment, nitrate or nitrite is added at a molar C/N
ratio of about 6/1, wherein C is carbon from the carbon/energy source and
N is nitrate or nitrite nitrogen. In another embodiment, the C/N ratio is
about 12/1, and in yet another embodiment, the C/N ratio is about 25/1.
microorganism water in the holding tank can be mixed, for example by
recirculating the water at 1 tank volume/day.

[0039]In another embodiment favoring aerobic populations, a nitrate or
nitrite salt is added where the total addition of nitrate and/or nitrite
is equivalent to approximately 0.4 g per liter as nitrogen. As described
above, the molar C/N ratio is at least about 6/1. In another embodiment,
the C/N ratio is about 12/1, and in yet another embodiment, the C/N ratio
is about 25/1. Sodium, potassium, calcium, magnesium, or other soluble
salts of nitrate or nitrite may be used individually or in combination.
In addition, a jet diffuser or similar device can be used to provide air
to the liquid in the holding tank, for example at a rate of 1-3 m3
air/m3 liquid per day.

[0040]In one embodiment, the hydrocarbon-exposed surface water does not
require supplementation with either a carbon/energy source or a nitrogen
source. For example, the water can be determined to contain the correct
C/N ratio, and thus can be incubated as necessary to induce the formation
of surface-active agents without additional supplementation.
Alternatively, the water can contain the desired level of surface-active
agents and can be used directly as conditioned water. The amount of
surface-active agent present in the surface water can be determined or
approximated by any suitable means, such as by using the emulsion
stability time test as described below.

[0041]Additional conditions, well known to those skilled in the art of
microbiology, must be met in order to obtain successful microbial growth
and production of surface-active agents in the holding tank. For example,
the pH of the water in the holding tank should be maintained at a pH
suitable for surface-active agent production, typically between
approximately pH 4 and pH 9. The temperature of the water in the holding
tank will typically be maintained between about 20° C. and
50° C. Typically the surface water is incubated for at least about
2 days to allow microbial growth and surface active agent production.

[0042]From embodiments above, one skilled in the art will recognize that
to achieve the desired level of surface-active agents in the
hydrocarbon-exposed surface water, it is necessary to determine and/or
monitor a number of parameters. The length of incubation time in the
holding tank during which the microorganisms grow and produce
surface-active agent will be in part dependent on the number of
surface-active agent producing microorganisms originally present in the
water. Lower initial numbers of microorganisms are expected in production
well, injection well, injector well, or interceptor well water. Higher
initial numbers, and possibly also higher nutrient levels, are expected
in wastewaters and runoff waters. By selection of the appropriate
hydrocarbon-exposed surface water having an exogenous mixed microbial
population, supplementing said water if necessary, and optimizing
incubation if necessary relative to temperature, pH, aeration and mixing,
the desired level of surface-active agents will be achieved.

[0043]To monitor the production of surface-active agents, samples can be
withdrawn from the holding tank daily and tested for the presence of
surface-active agents by any means known to those skilled in the art. In
one embodiment, the relative level of surface-active agents is determined
using tensiometry, and in another embodiment the emulsion stability time
test can be used. In one embodiment, the emulsion stability time test is
carried out by adding a light hydrocarbon such as
2,2,4,4,6,8,8-heptamethylnonane, hexadecane or five-weight motor oil, 2
mL, to 8 mL of holding tank water. The two-phase mixture is shaken
vigorously in a prescribed manner for a time sufficient to mix the two
phases, such as 30 seconds, and then put aside. The time required for the
emulsion to separate is recorded.

[0044]When the surface-active agent reaches a desired level, the water is
considered conditioned and can be injected into the
hydrocarbon-containing site. In one embodiment, the desired level of
surface-active agent is the maximal level achievable. The maximal level
can be estimated using the emulsion stability time test, wherein when the
time for the emulsion to separate reaches a maximum, the level of
surface-active agents produced in the surface water is expected to be at
a maximum.

[0045]For injection at a subsurface hydrocarbon-contaminated site, the
process of the invention can be carried out according to the following
embodiment. Conditioned water can be produced according to embodiments of
the present invention at the site of a clean-up of subsurface
contamination via remediation. When emulsion stability time is at a
maximum, the conditioned water is ready for injection through the
injector well. After connecting the holding tank with conditioned water
to the injector well water flow, the mixture is pumped into the
subsurface site. The rate of addition of the conditioned surface water is
maintained such that the increase in the injector well backpressure is
less than or equal to about 20% of the initial backpressure. As this
limit is approached, metering of the conditioned surface water into the
injector well is stopped. Injection water flow is allowed to continue.
Once backpressure drops to below 10% above the initial backpressure,
metering of the conditioned water into the injector well is restarted. In
this manner, the conditioned water is pumped into the site via the
injector well without causing loss of injectivity at the
hydrocarbon-contaminated site face. Remediation of the contaminant is
accelerated as a result of pumping the conditioned water through the
contaminated formation.

EXAMPLES

[0046]The present invention is further defined in the following Examples.
It should be understood that these Examples, while indicating preferred
embodiment of the invention, are given by way of illustration only. From
the above discussion and these Examples, one skilled in the art can
ascertain the essential characteristics of this invention, and without
departing from the spirit and scope thereof, can make various changes and
modifications of the invention to adapt it to various uses and
conditions.

[0047]In the following examples, "° C." is degrees Centigrade, "mg"
is milligram; "kg" is kilogram; "g" is gram; "pg" is microgram; "mL" is
milliliter; "L" is liter; "mMolar" is millimolar; "μM" is micromolar;
"mm" is millimeter; "rpm" is revolutions per minute; and "h" is hour.

General Methods

[0048]Water samples were obtained from oil well sites of the North Slope
of Alaska. They were held at approximately 0° C. on wet ice and
returned to the laboratory within one week. In the laboratory water
samples used for experiments were held at 4° C. under anoxic
conditions. These water samples were used to inoculate experimental test
systems in the laboratory. Incubations were done at room temperature
under anaerobic, denitrifying conditions with shaking at approximately
125 rpm. All test systems were two-phase with an upper hydrocarbon phase
and a lower aqueous medium phase. The upper hydrocarbon phase contained
either crude oil from the North Slope of Alaska or
2,2,4,4,6,8,8-heptamethylnonane (HMN). HMN is a non-metabolizable
hydrocarbon used as a surrogate for crude oil. As a transparent
hydrocarbon, rather than darkly colored, like crude oil, it allows better
visualization of the emulsion with water. North Slope water samples
containing mixed microbial populations were inoculated into mineral
medium 1 (Table 1) at a volume ratio of approximately one part water
sample to nine parts mineral medium. Incubations lasted approximately 8
to 21 days. The production of surface-active agents by the microorganisms
was monitored in one of two ways. In one method, the emulsion formed as a
result of the constant shaking was measured in vials set aside without
movement. The vial was oriented upright in the dark and the decrease in
the height of the emulsion and any changes in appearance were monitored
over 48 hours. In another method, the two phases in the vial were first
allowed to separate after removal of the vial from the shaking incubator.
The vial was then shaken in a prescribed manner, which can be described
as 20 up-and-down motions of 6 inches length done in 20 seconds with the
vial inverted. The vial was then set upright and left motionless. The
decrease in the height of the emulsion was monitored over time. The time
at which no separated emulsion particle remained was recorded as the
emulsion stability time.

[0049]Nitrate and nitrite analysis was performed using ion exchange
chromatography (IC) on an ICS2000 chromatography unit (Dionex,
Banockburn, Ill.). Ion exchange chromatography was performed on an AS15
anion exchange column using a gradient of potassium hydroxide.

The Effect of Various Supplements on the Production of Surface-Active
Agents

[0050]Microbial inocula from production water from a North Slope oil well
were added to mineral medium #1. The effect of various supplements on the
production of surface-active agents was determined. A surrogate oil phase
consisting of 1.4% decane, 1% naphthalene, 1% decalin and 96.6% HMN was
used in this experiment. Microbial growth occurred under anaerobic,
denitrifying conditions at room temperature with shaking at 125 rpm.
Analysis of nitrate and nitrite concentrations showed that microbial
denitrification was most rapid in treatments receiving acetate. After
eight days of growth, emulsification was apparent in a number of the
treatments. After allowing the oil-aqueous mixtures to stand for 42 h, a
significant emulsion layer remained, except in the control treatment
lacking both added supplement and microbial inoculum. This shows that
emulsions formed by microbial activity were quite stable. Results in
Table 3 show that when supplemented with acetate, the microorganisms in
production water were most effective at improving oil-water
compatibility. The emulsion layer was thickest, 14 mm, in the acetate
treatment. In addition, emulsion droplet size was smallest in the acetate
treatment, indicating greater emulsion stability in the acetate
treatment. This is evident in FIG. 1, which shows vials 1-4 containing
treatments 1-4, respectively. Treatment 1, containing microorganisms but
no added carbon/energy source, had the lowest emulsion height and
relatively course emulsion particles. Treatment 3, containing
microorganisms and sodium acetate as the main carbon/energy source, had
the highest emulsion height at 14 mm and also showed fine emulsion
particle formation. Treatment 2, which had yeast extract added as the
carbon/energy source showed an emulsion height of 10 mm and relatively
coarse emulsion particles. Treatment 4, absent any addition of
microorganisms or carbon/energy source, did not develop any emulsion.

The Effect of Various Supplements on the Production of Surface-Active
Agents

[0051]Two treatments were tested in triplicate, to examine the effect of
these treatments on the emulsification of crude oil. Non-sterile oil, 10
mL, from the North Slope was combined with 45 mL of mineral medium #1. As
shown in Table 4, sodium acetate was added to a final concentration of 2
g per liter in Test Treatment #2. No acetate was added to Test Treatment
#1. In addition, 1 mL of supernatant from treatment number 3 in Example 1
was added to Test Treatment #2. After 10 days, the level of the
emulsification was measured in the two sets of treatment vials. The
thickness of the emulsified layer was measured 30 minutes after vigorous
shaking. As shown in Table 4, the combination of microorganisms from
oil+treatment vial 3, example 1 with acetate supplementation developed
greater emulsion thickness than the vial without acetate and
microorganisms. This example shows that microorganisms causing
emulsification of oil surrogates are also effective in emulsification of
crude oil. Emulsion droplet size was not measured, because the darkness
of the oil prevented accurate measurement.

The Effect of Various Carbon and Energy Sources on the Production of
Surface-Active Agents

[0052]A variety of carbon and energy sources were tested for their ability
to cause endogenous microorganisms from North Slope injection water to
generate surface-active compounds. Different carbon/energy supplements
were tested for their ability to induce emulsification. Microbial growth,
aided by these supplements, occurred under anaerobic, denitrifying
conditions at room temperature. The hydrocarbon, HMN, was used as the oil
phase in this experiment. To test the resultant emulsifying capability of
the treatments, vials were vigorously shaken for 20 seconds to generate
an emulsion layer. The time to disappearance of emulsion layer was then
measured. FIG. 2 shows an example of this measurement sequence. In all
treatments except controls, which did not receive either carbon/ energy
supplement or carbon and energy source with nitrate, the stability of the
emulsion improved over time with microbial growth (Table 5). By day 22
sodium propionate, treatment 2, showed the greatest emulsion stability
time, 86 seconds, more than 6-fold greater than control treatments 6 and
7. All supplement treatments caused at least a 2-fold increase in
emulsion stability time over the controls.

The Effect of Various Supplements on the Production of Surface-Active
Agents

[0053]A variety of carbon and energy sources were tested for their ability
to cause endogenous microorganisms from North Slope production water to
generate surface-active compounds. Different carbon energy supplements
were tested for their ability to induce emulsification. Microbial growth,
aided by these supplements, occurred under anaerobic, denitrifying
conditions at room temperature. The hydrocarbon
2,2,4,4,6,8,8-heptamethylnonane was used as the oil phase in this
experiment. To test the resultant emulsifying capability of the
treatments, vials were vigorously shaken for 30 seconds to generate an
emulsion layer. The time to disappearance of emulsion layer was then
measured. In all treatments except controls, which did not receive either
carbon/energy supplement or carbon and energy source with nitrate, the
stability of the emulsion improved over time with microbial growth (Table
6). By day 22, sodium propionate, Treatment #2, showed the greatest
emulsion stability time, 198 seconds, more than 3-fold greater than
control treatments 6 and 7. All supplement treatments caused an increase
in emulsion stability time relative to the controls.

Application of the Exogenous Surface-Active Agent Water Conditioning
Technology to Accelerated Bioremediation

[0054]The techniques demonstrated in the examples above can be used in
field situations to improve the rates of contaminant degradation in
situations using remediation of hydrocarbon contaminated subsurface sites
in situations where water injection is in use.

[0055]An injector well is typically used to force water into the
contaminated subsurface formation. This allows agents that aid in
contaminant removal to be added to the groundwater in the formation. To
prevent movement of contamination off site, interceptor wells also
withdraw water from the contaminated formation. The combination of
injector and interceptor wells controls ground water flow in the
contaminated subsurface formation.

[0056]A 9000-gallon (34,000 liters) tanker truck is brought to the site of
contamination to serve as a convenient holding tank. Connections are made
to the injector and interceptor well pipelines. A 20 horsepower
recirculating water pump is also connected to the tank in order to allow
mixing of the tank. 30,000 liters of interceptor water are added to the
tank. Sodium propionate, 4400 pounds (1996 kg), is added and dissolved
into the tank water. Sodium nitrate, 900 pounds (408 kg), is added and
dissolved into the tank water. The tank is filled to capacity with
interceptor water. The tank is mixed intermittently, preferably totaling
at least 6 hours each day. Production of surface-active agents is
monitored daily by measuring emulsion stability time as described in the
detailed description of the invention.

[0057]When emulsion stability time is at a maximum, the contents of the
tank are metered into the injection water pipeline in a manner that
prevents loss of injectivity in the injector well. The surface-active
agents produced by the exogenous microorganisms are thus distributed into
the contaminated site. The addition of the surface-active agents is
expected to result in accelerated contaminant removal.

[0058]From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention and, without
departing from the spirit and scope thereof, can make various changes and
modifications to the invention to adapt it to various usages and
conditions.